The present invention relates to a magnetic recording, reproducing and erasing head. More particularly, it relates to a magnetic head well-suited for high density recording, reproducing and erasing, the core material of which is a metallic ferromagnetic material and the track width narrowing grooves of which are filled with glass.
A magnetic head for high density recording has heretofore had a structure wherein a metallic ferromagnetic material exhibiting a high saturation flux density is used as the material of a magnetic core, a transducing gap is narrowed in order to raise a linear recording density, and a core width is narrowed in order to raise a track density. When note is taken of the track width of the magnetic head, a conventional narrow-track magnetic head adopts an expedient in which, from the viewpoints of the magnetic reluctance, life as abrasion-resistance, mechanical strength, etc. of the core, the magnetic core width is left broad, and grooves for narrowing are provided in only necessary parts near the transducing gap so as to establish a required track width. The narrowing grooves are filled with glass of high reliability as a nonmagnetic material.
In such a magnetic head, when the track width narrowing grooves are directly filled with the glass, the reaction between the metallic ferromagnetic material and the glass poses the problem of deterioration in the characteristics of the ferromagnetic material. Especially when the ferromagnetic material is a film forced by a thin film formation technique, the reaction thereof with the glass becomes more severe than in case of a bulky material.
To cope with this, there has been proposed, for example, a method wherein, as disclosed in the official gazette of Japanese Patent Application Laid-open No. 56-124111, a film of high-melting material such as SiO, SiO.sub.2 or high-melting glass having a thickness of several thousand .ANG.--several .mu.m is deposited as a protective film between the metallic ferromagnetic material and the filling glass.
In the official gazette of Japanese Patent Application Laid-open No. 60-125909, in view of an insufficient wettability between the metallic ferromagnetic material and the glass, a method has been proposed in which the track width narrowing grooves of the magnetic head employing the metallic ferromagnetic material are provided with metal films and oxide films, whereupon the glass is packed on the oxide films. Also, the same sorts of constituents are disclosed in the official gazette of Japanese Patent Application Laid-open No. 59-142716 corresponding to U.S. Pat. No. 4,559,872.
FIG. 5 is a plan view which shows the recording medium-engaging face of a prior-art magnetic head of Japanese Patent Laid-Open No. 56-124111 employing metallic ferromagnetic films. The magnetic head is constructed of two magnetic core halves 15, 15' and a coil winding which is not shown. Each core half is made of a composite material consisting of ferrite 10 as a protective core and a metallic ferromagnetic film 11, and the track width narrowing grooves thereof are filled with glass 12 so as to form a reinforced structure. The core halves 15, 15' are joined through a nonmagnetic film 14 for a transducing gap. In the process of manufacturing the magnetic head, the metallic ferromagnetic films 11 are formed on the slant surfaces of the ferrite substrates 10, and the glass 12 is thereafter molten and packed. On this occasion, the glass 12 reacts with parts of the metallic ferromagnetic films 11 to deteriorate the magnetic characteristics of the metallic ferromagnetic films. Therefore, films 13 of high-melting material such as SiO, SiO.sub.2 or high-melting glass at a thickness of several thousand .ANG.--several .mu.m are previously deposited as protective films after the deposition of the metallic ferromagnetic films, and they are used as films for preventing of the reaction between the metallic ferromagnetic films and the glass.
This method, however, has the following disadvantages:
(1) Bubbles are produced by the reaction between the glass and the protective film. The bubbles are confined in the glass and appear as holes on the recording medium-engaging face, so that they form a cause for damaging a recording medium.
(2) When the protective oxide film is thinner than several .mu.m, the difference between the coefficient of thermal expansion of the protective oxide film and that of the metallic ferromagnetic film or the core material is not a serious problem. Hence, the range of selection for protective oxide materials widens, but the thickness is insufficient as the reaction preventive film. Consequently, the reaction layer of the protective film with the glass gets to the metallic ferromagnetic film and degrades the characteristics thereof.
(3) On the other hand, when the protective oxide film is formed thicker than several .mu.m so as to prevent the reaction layer from getting to the metallic ferromagnetic film, the difference between the thermal expansion coefficient of the protective film and that of the glass cannot be neglected, and the glass cracks. Moreover, the amount of the bubbles increases.
FIG. 6 is a plan view of the recording medium-engaging face of a magnetic head for illustrating another prior-art example disclosed in Japanese Patent Laid-open No. 60-125909 mentioned above. This magnetic head is constructed of two core halves 15, 15' which are made of a metallic ferromagnetic material (for example, Sendust) 11'. The core halves are provided with cut grooves for narrowing a track width in the vicinity of a transducing gap, and are unitarily joined through the transducing gap 14. The joining is effected by packing glass 12. In order to enhance the close contact and the joint strength between the metallic ferromagnetic material 11' and the glass 12, the prior-art example employs a structure in which nonmagnetic metal films 16 are deposited on the glass packing grooves and are overlaid with oxide films 13, whereupon the glass is packed.
Thus, an adhered chain of materials exhibiting great affinities of the adhesion between the metallic ferromagnetic material 11' such as the alloy Sendust and the nonmagnetic metal film 16, between the nonmagnetic metalfilm 16 and the metal oxide film 13, and between the metal oxide film 13 and the glass 12 is obtained. Accordingly, the mechanical strength of the filling glass and the joint strength of the core halves become very high.
Even with the above structure, however, the following disadvantages have been found:
Likewise to the preceding prior-art example, the metal oxide film 13 exists at the surface on which the glass 12 is packed, so that bubbles are produced by the reaction. On the other hand, when a metal oxide film not reacting with the glass is formed, the bonding strength is inferior, and the glass comes off.